This invention relates to a voltage amplifier circuit, and more particularly a voltage amplifier circuit especially suitable for use in an output circuit of a CCD (Charge Coupled Device) image sensor.
This invention also relates to an image pickup device, including the voltage amplifier circuit.
The CCD image sensor has been widely used as a semiconductor element for converting an optical image signal into an electric signal. For example, a CCD linear image sensor, including linearly arranged pixels, is an indispensable component as a light receiving element for reading picture images in facsimile devices and photocopying machines, etc.
A CCD linear image sensor is made up of a pixel array, including a plurality of linearly arranged pixels, CCD registers for temporarily holding electric charges generated by respective pixels for transferring, and shift gate circuits for transferring charges of the pixels array to the CCD registers. The signal charges transferred by the CCD registers are stored in floating-diffusion capacitors acting as charge accumulators, and a voltage variation thereof is detected by a source follower in the succeeding stage. This voltage variation is amplified by a voltage amplifier circuit for increasing the sensitivity and then outputted as a low impedance voltage output signal.
The voltage amplifier circuit is constituted by a plurality of inverter circuits and source follower circuits. Such a voltage amplifier circuit is formed on a chip together with the CCD sensor by taking into consideration decreases in cost and noise.
In a prior art voltage amplifier circuit, however, there are many problems that the circuit construction is complicated and the operating speed decreases, etc., caused by the relation between the linear input voltage range of the source follower in the previous stage and the operating point of the inverter.